Hi Darren,
What a bad situation. I'm sorry, sorry you've had to go through this.
I've read experiences of other people involved with Ns, and this is so typical -- people think the actual victim is to blame and the N is the greatest person on earth. Then, most of the time, eventually "murder will out", as my mother (and Shakespeare) used to say, and they find out who the real abuser is.
I don't think it has to be an N or even a person with strong personality disorder traits of any kind -- I think eventually, people show their true colors.
It sounds like your heart is tugging at you -- but you do not owe any of these people anything. You do not owe your ex anything; you do not owe her latest ex anything; you don't owe her friends anything; and, although this may seem cruel, you don't owe that child anything. The child thing is their battle, not yours.
That may all sound very harsh -- and so may this -- but I really think the best thing for you is to put them in the past and move on with your life. If they need to, they'll subpoena you as a witness and then you can go. But your real job is to focus on you, your life, your healing, your building a new life.
I know this is a tougher "take" than others have said, but ... I'm pretty sure it's what my therapist would tell you. (Based on lots of experience with me and my fellow group members.)
But I hear the hurt, and your desire to reach out and help is very commendable and wonderful.
Best,
LC